13,028 research outputs found
Mode coupling theory for the critical dynamics of dipolar ferromagnets Hyperfine Interactions
Scaling function for the noisy Burgers equation in the soliton approximation
We derive the scaling function for the one dimensional noisy Burgers equation
in the two-soliton approximation within the weak noise canonical phase space
approach. The result is in agreement with an earlier heuristic expression and
exhibits the correct scaling properties. The calculation presents the first
step in a many body treatment of the correlations in the Burgers equation.Comment: Replacement: Several corrections, 4 pages, Revtex file, 3 figures. To
appear in Europhysics Letter
Electron-Hole Crossover in Graphene Quantum Dots
We investigate the addition spectrum of a graphene quantum dot in the
vicinity of the electron-hole crossover as a function of perpendicular magnetic
field. Coulomb blockade resonances of the 50 nm wide dot are visible at all
gate voltages across the transport gap ranging from hole to electron transport.
The magnetic field dependence of more than 50 states displays the unique
complex evolution of the diamagnetic spectrum of a graphene dot from the
low-field regime to the Landau regime with the n=0 Landau level situated in the
center of the transport gap marking the electron-hole crossover. The average
peak spacing in the energy region around the crossover decreases with
increasing magnetic field. In the vicinity of the charge neutrality point we
observe a well resolved and rich excited state spectrum.Comment: 4 pages, 3 figure
Physical limitations to the spatial resolution of solid-state detectors
In this paper we explore the effect of -ray emission, fluctuations in
th e signal deposition on the detection of charged particles in silicon-based
detec tors. We show that these two effects ultimately limit the resolution that
can be achieved by interpolation of the signal in finely segmented
position-sensitive solid-state devices.Comment: 5 page
Renal handling of prednisolone/prednisone: effect of steroid dose and llβ-hydroxysteroid dehydrogenase
The purposes of this study were: (1) to determine under steady-state conditions whether the renal clearance of prednisolone is concentration dependent, and (2) to establish whether the urinary excretion of prednisolone and its biologically inactive 11-dehydro metabolite prednisone depend upon the activity of 11β-hydroxysteroid dehydrogenase (11β-OHSD). For that purpose 10 healthy volunteers were infused to steady state over a 13-h period either at a low (11 μg/h × kg) or a high (70 μg/h × kg) rate with prednisolone on two occasions, once without and once with administration of glycyrrhetinic acid, an inhibitor of 11β-OHSD. Prednisolone and prednisone were measured by high-pressure liquid chromatography. Mean renal clearance values of total or unbound prednisolone were several times higher during the high than the low infusion rate. The fractional renal clearance of unbound prednisolone during the high, but not during the low infusion rate exceeded 1. This indicates that in addition to unbound prednisolone, protein-bound prednisolone is excreted in urine at high plasma concentrations. Inhibition of 11β-OHSD increased the urinary ratios of prednisolone/prednisone in all subjects. Conclusions: (1) The renal clearance of prednisolone is concentration dependent; (2) there must be tubular secretion and/or glomerular filtration of prednisolone bound to plasma proteins; (3) the urinary excretion of prednisolone/prednisone is modulated by the activity of 11 β-OHS
Evaluation of electrode shape and nondestructive evaluation method for welded solar cell interconnects
Resistance welds of solar cell interconnect tabs were evaluated. Both copper-silver and silver-silver welds were made with various heat inputs and weld durations. Parallel gap and annular gap weld electrode designs were used. The welds were analyzed by light microscope, electron microprobe and scanning laser acoustic microscope. These analyses showed the size and shape of the weld, the relationship between the acoustic micrographs, the visible electrode footprint, and the effect of electrode misalignment. The effect of weld heat input on weld microstructure was also shown
Pair distribution function and structure factor of spherical particles
The availability of neutron spallation-source instruments that provide total
scattering powder diffraction has led to an increased application of real-space
structure analysis using the pair distribution function. Currently, the
analytical treatment of finite size effects within pair distribution refinement
procedures is limited. To that end, an envelope function is derived which
transforms the pair distribution function of an infinite solid into that of a
spherical particle with the same crystal structure. Distributions of particle
sizes are then considered, and the associated envelope function is used to
predict the particle size distribution of an experimental sample of gold
nanoparticles from its pair distribution function alone. Finally, complementing
the wealth of existing diffraction analysis, the peak broadening for the
structure factor of spherical particles, expressed as a convolution derived
from the envelope functions, is calculated exactly for all particle size
distributions considered, and peak maxima, offsets, and asymmetries are
discussed.Comment: 7 pages, 6 figure
Review of Top Quark Physics
We present an overview of Top Quark Physics - from what has been learned so
far at the Tevatron, to the searches that lie ahead at present and future
colliders. We summarize the richness of the measurements and discuss their
possible impact on our understanding of the Standard Model by pointing out
their key elements and limitations. When possible, we discuss how the top quark
may provide a connection to new or unexpected physics.Comment: 84 pp. With permission from the Annual Review of Nuclear & Particle
Science. Final version of this material is scheduled to appear in the Annual
Review of Nuclear & Particle Science Vol. 53, to be published in December
2003 by Annual Reviews (http://www.annualreviews.org
Nonaffine rubber elasticity for stiff polymer networks
We present a theory for the elasticity of cross-linked stiff polymer
networks. Stiff polymers, unlike their flexible counterparts, are highly
anisotropic elastic objects. Similar to mechanical beams stiff polymers easily
deform in bending, while they are much stiffer with respect to tensile forces
(``stretching''). Unlike in previous approaches, where network elasticity is
derived from the stretching mode, our theory properly accounts for the soft
bending response. A self-consistent effective medium approach is used to
calculate the macroscopic elastic moduli starting from a microscopic
characterization of the deformation field in terms of ``floppy modes'' --
low-energy bending excitations that retain a high degree of non-affinity. The
length-scale characterizing the emergent non-affinity is given by the ``fiber
length'' , defined as the scale over which the polymers remain straight.
The calculated scaling properties for the shear modulus are in excellent
agreement with the results of recent simulations obtained in two-dimensional
model networks. Furthermore, our theory can be applied to rationalize bulk
rheological data in reconstituted actin networks.Comment: 12 pages, 10 figures, revised Section II
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